1. Field of the Invention
The invention lies in the technical field of siloxanes, and in particular of polyorganosiloxanes also commonly known as silicones. More specifically, the present invention relates to hydrosilylation reactions, also known as polyadditions, of an unsaturated compound with a siloxane comprising at least one hydrogen atom bonded to a silicon atom.
2. Description of Related Art
In the field of silicones, hydrosilylation is a major reaction.
During a hydrosilylation reaction, a compound comprising at least one unsaturation reacts with a compound comprising at least one hydrogen atom bonded to a silicon atom. This reaction can, for example, be described by the reaction equation (1) in the case of an unsaturation of alkene type:
or by the reaction equation (2) in the case of an unsaturation of alkyne type:

Hydrosilylation therefore makes it possible to bond siloxanes, and in particular silicones, comprising Si—H units, with compounds that have at least one unsaturation of alkene or alkyne type, for example silicones comprising Si-vinyl units.
Hydrosilylation reactions are conventionally carried out by catalysis. Typically, the catalyst appropriate for this reaction is a platinum catalyst, such as, for example, chloroplatinic acid hexahydrate or the Karstedt catalyst which consists of platinum complexes with divinyltetramethyldisiloxane as ligand (see, for example, in U.S. Pat. No. 3,775,452).
However, the use of a platinum catalyst is problematic. It is in fact preferable to avoid the use of platinum on an industrial scale since it is an expensive metal which is becoming increasingly scarce and the cost of which fluctuates enormously. As a result, the cost of siliceous compounds produced by hydrosilylation, such as siloxanes and polyorganosiloxanes functionalized by hydrosilylation and silicone compositions crosslinkable by hydrosilylation, is indexed to the cost of platinum, which is worrying both for manufacturers and for their clients.
It would therefore be advantageous to have an alternative to the platinum-catalyzed hydrosilylation reaction. It would be quite particularly advantageous to provide a novel type of catalyst for siloxane hydrosilylation reactions not containing platinum.
The use of other catalysts has been proposed in the past, for example the use of rhodium or iridium. However, these metals are as rare as platinum, and the use thereof does not solve the problems mentioned. International patent application WO 2011/006044 describes the use of complexes of manganese, of iron, of cobalt or of nickel containing pyridine diimine ligands as hydrosilylation catalyst. In addition, the publication by D. A. de Vekki (“Hydrosilylation on Photoactivated Catalyst”, Russian Journal of General Chemistry, 2011, 81, 7, 1480-1492) describes photoactivatable catalysts for hydrosilylation of C═C, C≡C and C═O bonds.
One of the objectives of the present invention is therefore to provide a process for hydrosilylation between a siloxane compound and an unsaturated compound, which would use an advantageously inexpensive catalyst, which is easy to supply, which is easy to handle and/or which has a low toxicity or is non-toxic. In addition, it is desirable for the hydrosilylation yields obtained with this alternative catalyst to be as high as possible.
Moreover, the use of compounds of the polyoxometalate family, commonly called POMs, as a catalyst has been described in the literature. POMs are anionic clusters of transition metal oxides. The publication by D. Tzirakis et al. “Decatungstate as an efficient photocatalyst in organic chemistry” (Chemical Society Reviews, 2009, 38, 2609-2621) describes in particular the photochemical properties of POMs, and in particular of decatungstate, and the use thereof as a photocatalyst. This publication describes the use of decatungstate for the creation of carbon-carbon bonds by homolytic breaking of carbon-hydrogen bonds, for oxidation in the presence of oxygen and for degradation of organic pollutants.
More recently, the researchers Jacques Lalevée, Nicolas Blanchard, Mohamad-Ali Tehfe and Jean Pierre Fouassier have described, for the first time, in a publication entitled “Decatungstate (W10O324−)/Silane: a New and Promising Radical Source Under Soft Light Irradiation” (Macromolecular Rapid Communications, 2011, 32, 838-843), that decatungstate can be used as a photocatalyst for forming silyl radicals from silanes. The photopolymerization of epoxides has been presented as a concrete use of this property.
However, no application in hydrosilylation has been envisioned. In addition, these disclosures do not concern siloxanes, the reactivity of which is different than that of silanes.